This invention relates to a baghouse having filter bags therein for separating solid particles from a dust laden gas stream and more particularly to an improved individual suspension system for mounting each filter bag in the baghouse.
Typical baghouses and suspension systems for mounting the filter bags therein are shown in U.S. Pat. Nos. 3,881,673; 4,123,027; 4,217,117 and 4,481,022.
A baghouse, as is well known, comprises a gas tight housing having a gas impervious floor plate dividing the baghouse into a dirty gas chamber having a dirty gas inlet and a clean gas chamber having a clean gas outlet. The floor plate has a series of apertures which open into a dust receiving hopper or a series of hoppers which form part of the dirty gas chamber.
A plurality of filter bags, usually tubular and constructed of a fragile glass fabric, are suspended from a supporting framework in the clean gas chamber. The bottom of each filter bag is open and is secured in sealed relation around an associated aperture in the floor plate. The top end of each filter bag is closed and attached to the framework in the clean air chamber at the top of the housing by means of some type of spring suspension system which must be vertically extended to make the filter bags taut when they are installed.
A large baghouse installation could include 32 baghouses that are each 33 feet long, 18 feet wide, 80 feet high, have as many as 312 filter bags each 34 feet long by 12 inches in diameter, and process 2,000,000 cubic feet per minute (CFM) of dirty gas. The current cost of such a baghouse per se, can be $25,000,000. Baghouses have been in use for more than forty years and the unsolved problem is how to reduce the size of the baghouse and thus significantly reduce its cost without reducing its CFM capacity or its operational efficiency.
In each of the mentioned patents, the top end of each filter bag is connected to an internal supporting framework by an individual spring suspension system which is, as previously described, of the type which must be vertically lengthened when the filter bag is initially installed to place and maintain the filter bag under tension. Proper tension is necessary to prevent folding and creasing of the filter bag which reduces collection efficiency and causes premature failure of the fragile glass fabric. In U.S. Pat. Nos. 3,881,673 and 4,217,117, a linkage is vertically extended to place an associated spring in compression. In U.S. Pat. No. 4,123,027 the spring itself is vertically extended. In U.S. Pat. No. 4,481,022, the suspension system uses a helical coil torsion spring unit having angularly extending side arms. The helical coil is tensioned by increasing the angle between the spring side arms which extends the vertical length of the suspension system when the filter bag is installed.
In the prior art when a baghouse is designed, the increase in vertical length of the spring suspension system required for initial tensioning of the filter bags is calculated. Then the internal vertical height of the baghouse is increased by the length of vertical travel required at installation by the spring suspension system. In the past it was thought necessary that the baghouse height be increased beyond the theoretical minimum height to accommodate the increase in length of the suspension system because it has not been possible to eliminate the need for vertical travel in the spring suspension system.
This need for vertical travel exists because in operation, dust laden gas enters the dirty air chamber, travels upward and passes through the filter bags and clean gas outlet. Dust is trapped on the inside surfaces of the filter bags and builds up into a filter cake of dust which increases the weight of the filter bag and its resistance to gas flow. The filter bags must be cleaned periodically, usually every two to six hours depending on conditions. Cleaning is accomplished during a cleaning cycle by pulsing air in a reverse direction through the filter bag, flowing air in a reverse direction through the bags, shaking the bags or a combination of these methods. In each cleaning method, the spring suspension system must be allowed to extend to permit a limited collapse of the filter bag. If limited collapse is not permitted, the filter cake will not be completely dislodged and the filter bag will be only partially cleaned. If the filter bag is allowed to collapse too much, the bag will develop folds that close off the interior opening at the bottom of the bag and either prevent the filter cake from falling through to the hopper or leave an unreasonably narrow opening at some region or regions inside the bag which increases the velocity of the reverse gas stream in such narrowed regions. The dust in the gas stream makes it very abrasive. The high velocity abrasive gas stream will quickly wear through the filter bag fabric in the narrowed regions which experience the high velocity gas flow.
Therefore, the problem which has not been satisfactorily solved in the past is how to design a filter bag suspension system to always keep each filter bag taut that will:
(1) not require any extension of its vertical length when the filter bag is initially installed, (2) not require any extension of its vertical length as the weight of the filter bag increases due to buildup of dust filter cake to a maximum dust loaded weight, and (3) permit momentary vertical extension during a cleaning cycle to allow a predetermined amount of filter bag collapse for efficient cleaning so that the vertical height of the baghouse need not be unnecessarily increased as it has in prior art designs but can be kept to a theoretical minimum to significantly reduce cost.